Brush arrangement for an electric machine

ABSTRACT

A brush device for an electric machine having at least one brush and at least one element such as a helical, scroll, or plunger spring for pressing each brush against a rotating contact element, for example a commutator. In at least one further element for example a spring tab, counteracts a lifting of each brush away from the contact element. To this end, the spring tab is inclined at an angle, as a result of which it exerts a weaker action when the brush moves in the direction toward the contact element than it does counter to this direction. As a result, the brush can be repositioned, but is prevented from lifting away from the contact element. This also reduces the danger of vibrations.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a 35 USC 371 application Ser. No. of PCT/DE2004/001007 filed on May 14, 2004.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention is directed to an improved brush device for anelectrical machine.

2. Description of the Prior Art

A brush device of the type with which this invention is concerned has atleast one brush and at least one element for pressing the brush againsta preferably rotating contact element. As a rule, the pressing elementis a helical spring or a scroll spring. The contact element can be acommutator or a slip ring. The pressing element should reposition thebrush as it wears down and prevent it from lifting off, for example duethe contact element being out of round. The more powerful the pressingelement is designed to be, the less danger there is of a liftoff. Butthis also increases the wear. Finally, the necessary play in theguidance of the brush also permits the occurrence of undesirablevibrations due to fluctuations in the coefficient of friction.

SUMMARY AND ADVANTAGES OF THE INVENTION

The brush device for an electrical machine according to presentinvention has the advantage that it reduces the danger of the brushlifting away from the contact element. It permits a spring for pressingthe brush to be embodied in a weaker form, which has a positive effecton the wear. It is also possible to reduce vibrations due to therequired play in the guide. A more exact brush positioning is thuspossible, which results in a more precise commutation and reduced noise.To this end, the brush device for an electric machine, which has a brushand at least one element for pressing the brush against a preferablyrotating contact element, has an additional element that counteracts alifting of the brush away from the contact element. In this case, the atleast one element is preferably clamped at an end oriented away from thebrush and rests against the brush with its other end. It is advantageousif, between the ends of the at least one element, at least one firstsection is provided, which exerts a more rigid action counter to thepressing direction than it does in the pressing direction, i.e. the atleast one element provides more friction against the brush when itattempts to move away from the commutator than when the brush movestoward the commutator.

If noncircularities of the contact element require a certain residualflexibility, then a second section is provided between the at least onefirst section and the clamped end; this second section, at least in thedirection counter to the pressing direction, exerts a weaker action thanthe at least one first section and preferably exerts the same elasticaction both in and counter to the pressing direction.

If the brush-pressing element engages the brush obliquely in relation tothe pressing direction, then the brush is less likely to vibrate in itsguide.

In an inexpensive embodiment, the at least one pressing element isembodied as integrally connected to the at least one element.

If the contact element has only one rotation direction, then it isadvantageous to situate the at least one element on the side of thebrush oriented away from the rotation direction of the contact element.If the contact element has two different rotation directions, then it isadvantageous for the at least one element to rest against a side of thebrush situated in a plane with the rotation direction of the contactelement. However, the element can also rest against both of the sidesmentioned above.

In a preferred embodiment form, the at least one element is a springtab; the spring tab rests with one edge against the brush and a sectionadjoining this is inclined in the direction of the contact element. Inthis way, the at least one element lends more friction against the brushmoving away from the commutator than for the brush to move towards thecommutator.

In an advantageous modification, the at least one element is a springtab and the at least one pressing device is a scroll spring. In thisconnection, it is cost-effective for an element embodied in the form ofa spring tab and a scroll spring for pressing the brush against thecontact element to be connected to each other by means of a bracket.

An electric machine equipped with a brush device according to thepresent invention has the advantage that it can last longer because thebrushes wear down less quickly.

BRIEF DESCRIPTION OF THE DRAWINGS

Other features and advantages of the invention will become apparent fromthe detailed description contained herein below, taken in conjunctionwith the drawings, in which:

FIG. 1 shows a cross section through a brush device according to theinvention in an electric machine,

FIG. 2 shows a second, modified brush device,

FIG. 3 shows a third, modified brush device,

FIG. 4 shows a fourth, modified brush device,

FIG. 5 shows a longitudinal section through a fifth, modified brushdevice, and

FIG. 6 shows a longitudinal section through a sixth brush device,

DESCRIPTION OF THE PREFERRED EMBODIMENT

FIG. 1 is a simplified, cross-sectional depiction of a part of anelectric machine 10 more particularly a brush-equipped DC motor that canbe used, for example, in a power window, a wiper drive unit, etc. of amotor vehicle. It can, however, also be a generator.

For the case in which it is a brush-equipped DC motor, the shaft 12 ofthe electric machine 10 supports a commutator 14. In the case of agenerator, this would be a slip ring. In both cases, however, it is acontact element that preferably rotates.

A brush device 16.1 is also shown in the drawing. The brush device 16.1has the required number of brushes 18, but has at least one brush 18 andat least one sliding contact. The brush 18 is made of carbon or anothersuitable material; it is contained in a guide 20 in a sliding fashionwith play; the guide 20 is oriented toward the shaft 12 of the electricmachine 10 and its two side walls 21.1 and 21.2 are visible in thedrawing. The guide 20 is preferably part of a brush holder not shown infurther detail. An arrow that points toward the shaft 12 indicates thepressing direction 22 in FIG. 1. The brush device also has a helicalspring 24, which constitutes an element that presses the brush 18against the commutator 14. The helical spring 24 can rest against alimit of the guide 20 at its end oriented away from the commutator 14.

In addition to the helical spring 24, a spring tab 26.1 is alsoprovided, which rests against the brush 18 laterally and counteracts alifting of the brush 18 off of the commutator 14. To this end, thespring tab 26.1 is clamped at an end 28 oriented away from the brush 18.The end 28 can, for example, be integrally connected to the brushholder, not shown in further detail, as part of a plastic injectionmolding process. The spring tab 26.1 can, however, also be a metal partthat has been extrusion coated with plastic or can simply bepressed-fitted into place. With the other end 30 and its edge, thespring tab 26.1 rests against the brush 18. The section 32 of the springtab 26.1 adjoining the end 30 and its edge is inclined in the directionof the commutator 14 and the pressing direction 22. This means that thesection 32 has a higher coefficient of friction and exerts a more rigidaction counter to the pressing direction 22 than it does in the pressingdirection 22. Thus, the spring tab 26.1 provides greater resistanceagainst the brush 18 moving away from the commutator 12 than it does formovement of the brush 18 towards the commutator 12. The inclinationangle α between the pressing direction 22 and the section 32 is lessthan 90° and greater than 0°. Preferably, the angle lies in a range from60° to 80°; a particularly favorable angle has turned out to be 70°.However, standard production tolerances of a few degrees must be takeninto count.

Finally, the spring tab 26.1 shown in FIG. 1 is situated on the side 36of the brush 18 oriented away from the rotation direction of thecommutator 14 indicated by the arrow 34. As a result, during rotation,the spring tab 26.1 and the movement of the commutator 14 both act topress the brush 18 against the side wall 21.2. In FIG. 1, the spring tab26.1 is embodied so that it is virtually impossible for the brush 18 tomove counter to the pressing direction 22 since the inclination of thespring tab 26.1 provides a much greater coefficient of friction in thisdirection and thus prevents the brush from being deflected counter tothe pressing direction 22. Preferably, the spring tab 26.1 inhibits orprevents the brush 18 from moving counter to the pressing direction.This inhibiting action, however, can also be accompanied by a certainresidual elasticity. As the helical spring 24 repositions the brush 18as it wears down, the spring tab 26.1 can pivot slightly away from thebrush 18, although it is still able to rest against it. Care must betaken here to dimension the helical spring 24 so that it overcomes thespring force generated by the spring tab 26.1 and the friction in theguide 20.

FIG. 2 shows a modified spring tab 26.2. The remaining components arethe same and have been provided with the same reference numerals as inFIG. 1, and reference is made to FIG. 1 with regard to these parts.Between the first section 32 of the spring tab 26.2 and the clamped end28, there is a second section 38 that extends essentially perpendicularto the pressing direction 22. To this end, the spring tab 26 is bentbetween the two sections 32 and 38. As a result, the second section 38exerts a weaker action than the first section 32, at least in thedirection counter to the pressing direction 22, and consequently exertsan elastic action that is preferably equal both in and counter to thepressing direction 22. The second section 38 can also be inclined inrelation to the position shown. It is also possible to use the length 40of the second section 38 to influence the rigidity or elastic behaviorof the spring tab 26.2. The elastic behavior of the spring tab 26.2lends it a residual flexibility that is advantageous if the commutator14 is very out of round.

FIG. 3 shows a brush device 16.3, which has a modified brush 18′. Theremaining components are the same and have been provided with the samereference numerals as in FIG. 1, and reference is made to FIG. 1 withregard to these parts. The end 42 of the brush 18′ oriented away fromthe commutator 14 has a bevel 44. A scroll spring 46, for example,engages this bevel. The spring force thus acts obliquely to the pressingdirection 22 and obliquely to the brush 18′, which further stabilizesthe brush 18′ in its guide 20. The spring force acts in the samedirection as the rotation direction 34 of the commutator 14.

FIG. 4 shows a brush device 16.4. The only difference from the device inFIG. 3 is that the brush 18′ is rotated by 180° around its longitudinalaxis. As a result, the spring force of the scroll spring 46 acts counterto the rotation direction 34 of the commutator 14, which also stabilizesthe brush 18′ in the guide 20.

FIG. 5 shows a particularly inexpensive brush device 16.5. In thisinstance, the spring tab 26.3 and the scroll spring 46′ are embodied ofone piece. The spring tab 26.3 is connected to the scroll spring 46′ bymeans of a bracket portion 48. The bracket portion 48 has a firstsection 48.1 that adjoins the scroll spring 46′ and extends parallel tothe side wall 21.3 of the guide 20. The first section 48.1 is adjoinedby a second section 48.2 that protrudes out from the plane of the firstsection 48.1 and is situated in a lateral recess 50 in the side wall 21.The second section 48.2 is adjoined via an arc-shaped third section 48.3to the spring tab 26.3, which is oriented toward the brush 18′. Thesecond section 48.2 and the spring tab 26.3 thus enclose a V-shape thatis situated in the likewise V-shaped recess 50 of the side wall 21.3.The section 52 of the recess 50 that adjoins the end of the guide 20oriented toward the commutator 14 is farther away from the brush 18′than the remaining region of the side wall 21.3. This facilitatesinstallation of the brush device 16.5. It is naturally also possible toembody the recess in the form of a simple lateral through opening, etc.

Another aspect of the brush device according to FIG. 5 is that thespring tab 26.3 rests against the side 54 of the brush 18′ that lies ina plane with the rotation direction of the commutator 14. This isadvantageous in reversible electric machines 10. It is naturally alsopossible to embody or situate the spring tab 26 so that it rests againstboth this side 54 and the side 36 (FIG. 1).

FIG. 6 shows a brush device 16.6 equipped with a plunger spring 56 and abrush 18″ embodied in the form of a hammer brush. As elements thatcounteract a lifting of the brush 18″, bristles 60 are provided on asurface 58 oriented parallel to the pressing direction 22 of the plungerspring 56; these bristles 60 are inclined in relation to the pressingdirection 22 and rest against the plunger spring 56. As a result, theplunger spring 56 can move in the pressing direction 22, but isprevented or at least hindered from moving counter to the pressingdirection 22. The bristles 60 thus indirectly counteract a lifting ofthe brush 18″ via the plunger spring 56. The bristles 60 can also beprovided on both sides of the plunger spring 56; they can be comprisedof metal or plastic. In lieu of the bristles 60, it is also possible,for example, to provide a saw tooth geometry or a number of spring tabs.

In all of the above-mentioned elements 26.1, 26.2, 26.3, 60 thatcounteract a lifting of the brush 18, 18′, 18″, it is important thatthey exert a less rigid action in the pressing direction 22 than they docounter to the pressing direction 22. Preferably, they demonstrate aneven more rigid behavior counter to the pressing direction than thesprings 24, 46, 46′, and 56 themselves.

The foregoing relates to a preferred exemplary embodiment of theinvention, it being understood that other variants and embodimentsthereof are possible within the spirit and scope of the invention, thelatter being defined by the appended claims.

1. A brush device for an electric machine, comprising at least onebrush, at least one pressing element for pressing the at least one brushagainst a rotating contact element, and in addition to the at least onepressing element, at least one further element that counteracts alifting of the at least one brush away from the contact element, whereinthe at least one further element has a lower coefficient of friction andexerts less friction against movement of the brush in the pressingdirection than in the direction counter to the pressing direction,wherein said at least one further element comprises an elongated elementhaving two ends, and wherein between the two ends there is at least onefirst section (38) that exerts an equal action in both the pressingdirection and counter to the pressing direction.
 2. The brush deviceaccording to claim 1, wherein the at least one further element isclamped at an end oriented away from the at least one brush and itsother end rests against the at least one brush or against the pressingelement.
 3. The brush device according to claim 1, wherein said at leastone brush is retained in a guide, and wherein the at least one elementpresses the at least one brush against a side wall of the guide.
 4. Thebrush device according to claim 1, wherein the at least one furtherelement inhibits a movement of the at least one brush counter to thepressing direction.
 5. The brush device according to claim 1, furthercomprising a second section between the two ends which, and, at leastcounter to the pressing direction, the at least one first section exertsa weaker action than the second section.
 6. The brush device accordingto claim 1, wherein a surface of the rotating contact element approachesthe brush from one side of the brush, and the at least one pressingelement is situated on the side of the at least one brush which isoriented away from the one side and/or the at least one further elementrests against the one side of the at least one brush.
 7. The brushdevice according to claim 1, wherein the pressing element of the atleast one brush engages the at least one brush obliquely in relation tothe pressing direction.
 8. The brush device according to claim 1,wherein the at least one further element is a spring tab; wherein thespring tab rests with at least one edge against the at least one brush;and wherein an adjoining first section of the spring tab is inclined inthe direction of the contact element.
 9. An electric machine equippedwith a brush device according to claim
 1. 10. A brush device for anelectric machine, comprising at least one brush at least one pressingelement for pressing the at least one brush against a rotating contactelement, and in addition to the at least one pressing element, at leastone further element that counteracts a lifting of the at least one brushaway from the contact element, wherein the at least one further elementhas a lower coefficient of friction and exerts less friction againstmovement of the brush in the pressing direction than in the directioncounter to the pressing direction, wherein said at least one furtherelement comprises an elongated element having two ends, wherein betweenthe two ends there is at least one first section (38) that exerts anequal action in both the pressing direction and counter to the pressingdirection, and wherein the at least one further element is clamped at anend oriented away from the at least one brush and its other end restsagainst the at least one brush or against the pressing element.
 11. Thebrush device according to claim 10, further comprising a second sectionbetween the two ends which, and, at least counter to the pressingdirection, the at least one first section exerts a weaker action thanthe second section.
 12. The brush device according to claim 10, whereinthe pressing element of the at least one brush engages the at least onebrush obliquely in relation to the pressing direction.
 13. A brushdevice for an electric machine, comprising at least one brush at leastone pressing element for pressing the at least one brush against arotating contact element, and in addition to the at least one pressingelement, at least one further element that counteracts a lifting of theat least one brush away from the contact element, wherein the at leastone further element has a lower coefficient of friction and exerts lessfriction against movement of the brush in the pressing direction than inthe direction counter to the pressing direction, and wherein the atleast one pressing element is integrally joined to the at least onefurther element.
 14. The brush device according to claim 13, wherein thepressing element of the at least one brush engages the at least onebrush obliquely in relation to the pressing direction.
 15. A brushdevice for an electric machine, comprising at least one brush at leastone pressing element for pressing the at least one brush against arotating contact element, and in addition to the at least one pressingelement, at least one further element that counteracts a lifting of theat least one brush away from the contact element, wherein the at leastone further element has a lower coefficient of friction and exerts lessfriction against movement of the brush in the pressing direction than inthe direction counter to the pressing direction, wherein the at leastone further element is a spring tab and the at least one pressingelement is a scroll spring; and wherein the spring tab and a scrollspring are connected to each other by means of a bracket.